This invention relates to a superconducting magnetic field sensing apparatus, and more particularly, to a superconducting magnetometer or gradiometer apparatus having high bias margins and operable over a range of frequencies, including but not limited to frequencies greater than about 1 GHz.
A magnetometer is a device for measuring the intensity of a magnetic field in a particular direction. A gradiometer is a device for measuring the gradient of a magnetic field. In many applications, such as neuromagnetic imaging, highly-sensitive magnetic field readings are needed. One approach for achieving such high sensitivity is to use superconductive circuit elements.
Superconducting circuit elements such as superconducting quantum interference devices (SQUIDs) have been used for magnetometry purposes. Systems using such elements configured in analog fashion typically require external feedback circuitry which is usually bulky and expensive. Such feedback circuitry typically suffers from undesirably-limited slew rates.
The use of a SQUID for magnetometry purposes having on-chip feedback also is known. To provide high sensitivity, however, an impractically-high stability for the clock bias amplitude has been required in the past. Further, because the clock signal input to each respective SQUID would require individual fine tuning, it is impractical to couple a large array of such SQUIDs together for multi-channel magnetometry purposes, such as magnetic imaging. Accordingly, a more capable superconducting magnetic field sensing apparatus is needed.